A recent 15-year study of six large integrated health systems estimated 1.18 imaging tests per patient per year were performed in the United States, which amounts to an estimated 400 million imaging tests performed each year, at a cost of approximately $100 billion annually. Three quarters of these tests are performed in the ambulatory setting and although diagnostic imaging is predominantly non-invasive, it carries safety risks that could potentially harm patients. In addition, diagnostic errors are magnified when diagnostic imaging is utilized inappropriately and/or when there is no closed-loop system to monitor diagnostic follow-up. Thus, identifying contributing factors to diagnostic imaging failures in ambulatory care is of utmost importance. Cancer is one of the most common leading missed diagnoses in diagnostic litigation cases. Lung cancer is the leading cause of cancer deaths in the United States, followed by breast cancer in women. The most common suspicious abnormality for lung cancer on CT scan include lung nodules. Thus, standardized follow-up of lung nodules impacts early cancer detection, which provides the best chance for survival in lung cancer patients. Similarly, breast cancer screening is a mainstay of public health in the country with over 33 million women receiving mammograms each year. Recommendation for Breast Imaging Reporting and Data System (BIRADS) category 3 breast findings typically includes 6-month follow-up imaging. We therefore plan to assess suboptimal follow-up for patients with lung nodules and BIRADS category 3 breast findings. We propose a project that assesses diagnostic failures that are related to diagnostic imaging from two sources: (1) safety events related to all modalities of diagnostic imaging from an electronic safety reporting system, and (2) the institution's Patient Safety Net Initiative (PSNI), which combines Health Information Technology (HIT) and Care Coordination approaches for monitoring imaging follow-up. We focus on two specific aims to identify, characterize and evaluate contributing factors to diagnostic failures. These include (1) To measure the incidence of safety events that are related to diagnostic imaging from safety reports submitted to an electronic safety reporting system; and (2) To measure the incidence of suboptimal follow-up and comprehensively assess the impact of socio-technical factors on suboptimal diagnostic exam follow-up care in the ambulatory setting, specifically for two clinically significant findings with follow-up requirements: lung nodules and BIRADS category 3 breast findings. Diagnostic imaging in the ambulatory setting is influenced by socio-technical factors that contribute to performance of inappropriate exams as well as suboptimal follow-up care, all leading to diagnostic imaging failures. This study will identify these factors and assess their impact on diagnostic exam follow-up care in the ambulatory setting using the Patient Safety Net Initiative.